The invention relates to a valve drive for a gas exchange valve in an engine.
A whole series of valve drives of the type stated is known from the patent literature. In this connection, reference is hereby made to DE 101 25 767 C1.
The basic principle of this valve drive, which is already known from this patent, is that a rotor rigidly connected with the gas exchange valve is moved along the common axis in the magnetic field of a stator.
In order to produce sufficiently high forces on the rotor in an economical manner, correspondingly strong magnetic fields are needed in the air gap between the stator and the rotor. For this purpose, the air gaps in the magnetic circuit must be as small as possible, and suitable current coils must be positioned on the stator, among other features.
Furthermore, the actuator, which consists of the stator and the rotor, must fit into the relatively small construction spaces that are available, such as the cylinder head of a motor vehicle internal combustion engine, for example, for which reason the current coils and the active air gap surfaces can not be constructed as large as desired. The magnetic losses in the magnetic circuit must be kept low. In addition, the current and voltage are limited, even in the on-board power system of motor vehicles.
In the complex geometries on the cylinder head of an internal combustion engine, very exacting geometric tolerances must be observed between the individual function elements, particularly between the rotor and the stator of the valve drive, in order to prevent a jamming or an excessively large air gap.
Moreover, asymmetrical magnetic fields in the air gap on the rotor lead to considerable transverse forces, which are reinforced and can lead to excessively great frictional forces, energy losses, and even to the jamming of the rotor that has already been mentioned.
Since considerable temperature differences have to be taken into account on all engine components during the heating and cooling phase, especially in the case of internal combustion engines, and thereby thermally-induced changes in geometry as well (in the case of components made from materials with different thermal expansions and sharply differing temperatures), the air gaps and clearances must, for thermal reasons, be kept sufficiently large, particularly in the valve drive.
Accelerations of up to 100 times acceleration due to gravity act on gas exchange valves. These lead to excessively large component clearances and, in the air gap of the magnetic circuit, to an undesirable development of noise, asymmetrical forces, and abrasion in the valve drive.
In addition, particles from abrasion, wear and dirt, which are sometimes even magnetic, are always present in an internal combustion engine. These particles can also collect in the magnetic gaps of the actuator and lead to the jamming of the valve drive.
The connection of a gas exchange valve with the valve drive represents a considerable technical manufacturing problem, both in a power engine or a processing engine. That is to say, because of the local and functional conditions, the inspectability, the assembly, and the disassembly of the gas exchange valve and of the valve drive in the cylinder head must be guaranteed independently of one another.